CPU intensive tasks in KVM hangs host

Everytime i run an intensive task be it IO or CPU on the guest the entire machine hangs. I’ve stress tested hardware stability already on the host but when i start a game server or run prime 95 on the windows server guest, the entire machine hangs. I’ve tried changing various things to virto IO, threaded disk with no cache, including reducing the number of CPU threads for the guest but it still hangs when the physical CPU is fully used. Is there a way to put the guest CPU priority lower than host? I have encountered similar issues in the past where if i ran stress-ng on the host as root it would cause the machine to hang regardless of hardware setting but running it as user doesnt cause it to hang.

However KVM is run as root so whenever something intensive runs the whole thing hangs. I’ve never yet seen it survive a prolonged peak CPU or IO usage.

While virtualbox tends to be more stable, i need the memory performance.

Solved it, turned out the CPU fan had failed and the chpset required more volts for the IO.

This is the best kind of problem – one that you are able to solve yourself.

Thanks for reporting back.

Also, I wouldn’t say that virtualbox is likely “more stable” than KVM regarding CPU and memory.
Both are Gen2 Virtualization architectures which means that they access and utilize CPU extensions nearly the same way (The API is identical, what the app does with the the API might be different) for anything related to CPU and memory.

In other words, if the virtualization app makes same calls through the CPU extensions, you shouldn’t see much if any difference.

But, I/O (which likely includes your fan) is only in the process of becoming standardized.
Until complete, virtualized I/O and User Mode applications (like the GUI virtualization manager) are prime differentiators when selecting a virtualization technology.